Composition of matter

ABSTRACT

A WATER-SOLUBLE RUBBERY POLYMER, FORMED BY THE REACTION OF AN EPOXIDIZED WATER-INSOLUNLE NUETRAL RUBBERY POLYMER AND A WATER-SOLUBLE SECONDARY MONO AMINE, HAS PARTICULAR UTILITY IN THE FORMULATION OF WATER-SOLUBLE PRESSURE-SENSITIVE ADHESIVE AND COATINGS WHICH RENDER HYDROPHOBIC SUBSTRATES HYDROPHILIC.

United States Patent O US. Cl. 260-326 A 6 Claims ABSTRACT OF THEDISCLOSURE A water-soluble rubbery polymer, formed by the reaction of anepoxidized water-insoluble neutral rubbery polymer and a water-solublesecondary mono amine, has particular utility in the formulation ofwater-soluble pressure-sensitive adhesives and coatings which renderhydrophobic substrates hydrophilic.

CROSS-REFERENCES TO RELATED APPLICATIONS This application is a divisionof copending U.S. patent application Ser. No. 43,970, filed June 5,1970, now U.S. Pat. No. 3,661,874, which application was acontinuationin-part of Ser. No. 871,529, filed Nov. 6, 1969 and nowabandoned, which was, in turn, a continuation of Ser. No. 469,902, filedJuly 6, 1965, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to novelwater-soluble rubbery polymers and to compositions and products madetherewith.

There has long been a commercial appetite for compositions to primenormally hydrophobic surfaces and render them hydrophilic. By and large,rubbery polymers adhere well to hydrophobic surfaces, but they, too, arehydrophobic and hence not especially receptive to water-soluble orhydrophilic coatings.

Definition of terms As used herein rubbery means possessing thosephysical parameters (exclusive of solubility) which are used to define arubber as set out in ASTM Standard D '66-62T. The appropriate part ofthe definition given therein for rubber reads as follows:

A material that is capable of recovery from large deformations quicklyand forcibly A rubber retracts within one minute to less than 1.5 timesits original length after being stretched at room temperature (27 C.) totwice its length and held for one minute before release. All of thewater-soluble rubbery polymers of this invention meet this criterion.

As used herein, water-soluble means requiring 10-30 parts of water todissolve one part of solute; cf. Hackhs Chemical Dictionary, 3rdedition, McGraw-Hill (1944).

SUMMARY The present invention provides novel hydrophilic rubberypolymers which adhere firmly to both hydrophilic and hydrophobicsurfaces. These polymers, which are actually water-soluble, can also becompounded with tackifiers and used in the manufacture of water-solublenormally tacky and pressure-sensitive adhesives and other compositionshaving unique and valuable properties.

In accordance with the present invention, water-insoluble neutralrubbery polymers are rendered water-soluble by a comparatively simpletwo-step reaction in which a ice significant number of the double bondsin the rubbery material are converted to epoxy groups, and the epoxygroups thereafter reacted with secondary amine molecules to provide arubbery polymer characterized by the presence of tertiary amino groupsand hydroxyl groups. The resultant polymer is water-soluble, alkaline inaqueous solution, tough and leathery when dry, and still maintains asignificant degree of elasticity. Interestingly, whereas the originalrubbery polymers are soluble in a wide variety of organic solvents(e.g., methylene chloride, dioxane, toluene, benzene, and heptane), themodified water-soluble polymer is essentially insoluble in most organicsolvents. A preferred rubbery polymer for use in preparing materials inaccordance with the present invention is cis-1,4-polybutadiene, thedouble bonds in this polymer being especially susceptible toepoxidation. Other polymers are useful, however, as will be shown.

That organic solvent-soluble, water-insoluble rubbery polymers can bemade water-soluble and nonpolar solventinsoluble, without detractingfrom their high molecular weight, while still maintaining their rubberycharacteristics to a significant degree, is surprising. Thus, althoughnatural rubber has been wholly or partially epoxidized and thencross-linked with primary amines, the resultant product is less rubbery,and even more water-insoluble that it was before. Secondary amines, ofcourse, are not useful for this crosslinking reaction. Others have alsoreacted 2-methyl-2, 3-epoxy pentane, a model for natural rubber epoxide,with both primary and secondary amines, but there has been no suggestionthat the reaction product is water-soluble, let alone that rubber itselfcould be rendered water-soluble by epoxidation and reaction to an.appropriate extent with selected secondary amines.

Speaking in general terms, the more double bonds which are epoxidized,the greater the loss in rubbery characteristics sustained by thepolymer. Accordingly, it is generally preferred not to convert allunsaturation to epoxy rings. The requisite degree of epoxidation toobtain water-solubility is dependent upon both the specific rubberypolymer and the specific amine employed. Where the rubbery polymer iscis-1,4polybutadiene, the maximum epoxy equivalent (i.e., molecularweight per epoxy ring) to achieve water-solubility in a subsequentreaction with a secondary amine varies with the water solubility,stearic hindrance, etc. of such secondary amines. For example, where therubbery polymer is cis-1,4-polybutadiene and the secondary amine ismorpholine, the maximum epoxy equivalent (grams of polymer per epoxygram equivalent) has been found to be approximately 160. Where thesecondary amine is dimethyl amine, the maximum epoxy equivalent forachieving water solubility has been found to be approximately 210. Itappears that roughly the same figures apply when rubbery butadiene:styrene copolymers or rubbery butadienezacrylonitrile copolymers aresubstituted for polybutadiene. When dimethylamine is used withpolyisoprene, however, the maximum epoxy equivalent approaches 225.

Although a large number of secondary amines show utility in renderingepoxidized rubbery materials watersoluble, several general principles ofselection have proved significant. For example, the greater the watersolubility of the amine, the more effective it is in renderingepoxidized rubbery polymers water-soluble; hence, infinitelywater-soluble amines are generally preferred. Likewise, the lesssterically hindered the amino nitrogen, the more readily it reacts withan epoxy ring. For example, the presence of side chains or ring units onthe carbon atom adjacent the amino nitrogen is a great deterrent to thereaction. In the absence of steric hindrance, lower molecular weightsecondary amines tend to promote water-solubility more effectively thanhigher molecular 3 weight secondary amines, the reaction with epoxyrings occurring more rapidly, and the requisite degree of epoxidation ofthe rubbery polymer being lower. The more effective the secondary amineis in promoting watersolubility, the less the degree of epoxidationrequired.

Among the secondary amines which have been found effective in renderingepoxidized rubbery polymers water soluble aredimethylamine,diethylamine, diethanolamine, di-n-propylamine, di n butylamine,di-n-pentylamine, methylbenzylamine, methyl cycloh'exylamine,diallylamine, N-methylbenzylamine, N-methylcyclohexylamine,Z-ethylaminoethanol, morpholine, 2,6-dimethyl morpholine, piperidine,l-methyl piperazine, and pyrrolidine. it will be noted, that theforegoing list includes both saturated and unsaturated straight chainaliphatic compounds, cycloaliphatic compounds, and 6-member heterocycliccompounds, and secondary amines in which two different types ofsubstituent are attached to the amino nitrogen. Mixtures of secondaryamines may also be employed to take advantage of their individualproperties. Presence of certain groups in the vicinity of the aminonitrogen apparently inhibits or even prevents, the reaction with epoxygroups. For example, either the direct attachment of a benzene ring tothe nitrogen atom, or branching of an aliphatic substituent within twocarbon atoms of the amino nitrogen seems to prevent reaction with anepoxide ring. Thus, N-methyl aniline, diisopropylamine, anddiisobutylamine all perform more poorly than might be suspected. It isnoted that where the amino nitrogen is included in a heterocyclic ring,there appears to be essentially no problem of steric hindrance.

As previously indicated, water solubility of the finished product isaffected both by the nature of the secondary amine and the degree towhich it reacts with the epoxidized rubbery polymer. Where the polymeris cis-l, 4-polybutadiene, and where the secondary amine is morpholine,water solubility occurs when 1% or more nitrogen is introduced into thepolymer. Where the polymer is polyisoprene and the amine isdimethylamine, water solubility occurs With relatively extendedagitation when only 0.5% nitrogen is present in the polymer. Due to theextended reaction times necessary to both epoxidize and aminizepolyisoprene, the use of this rubber is not favored. Preferably,however, at least about 2 to 3% nitrogen is introduced into the polymer,thereby producing a polymer which is extremely useful in the manufactureof water-soluble normally tacky and pressuresensitive adhesives. Thepercent nitrogen necessary to achieve water solubility varies with thespecific amine employed; e.g., it will be somewhat lower fordimethylamine and somewhat higher for di-n-butylamine.

DESCRIPTION OF PREFERRED EMBODIMENTS The invention will be betterunderstood by reference to the following specific examples, which arepresented solely for the purpose of illustration.

EXAMPLE 1 Epoxidation of cis-l,4-polybutadiene In a 1-liter, three-neckround bottom flask equipped with stirrer, dropping funnel, thermometer,nitrogen inlet, and reflux condenser, was placed 540 grams (0.5 mol ofdouble bond) of a 5% solution of 1,4-polybutadiene in toluene. Thepolybutadiene contained approximately 98% cis configuration and hadaMooney viscosity (ML-4 at 212 F.) of about 41. This polymer, asavailable commercially from Goodrich-Gulf Chemicals Incorporated,Cleveland, Ohio, under the trade designation Ameripol CB-220, containsapproximately 1% 2,6-ditertiary butyl p-cresol stabilizer. Into theflask was also placed 6.0 grams of acidic ion-exchange resin (availablecommercially from the Dow Chemical Company under the trade designationas Dowex 50W-X12) which had been leached with acetic acid and dried withsuction on a sintered glass filter, the acetic acid content of thethus-dried resin being 17.6%. To the flask was then added 15.4 grams ofglacial acetic acid, making the total amount of acetic acid present0.2738 mol. The mixture was continuously stirred and heated at 60 C. for50 minutes, during which time 37.4 grams (0.55 mol) of 50% hydrogenperoxide was slowly added. Heating and stirring were then continued foran additional 5 hours, at the end of which time the rubber precipitated.The toluene was then poured off and suflicient 1,4-dioxane added todissolve the rubber. The rubber was again precipitated by adding thesolution to methyl alcohol, after which it was re-dissolved in methylenechloride to give an 8.73% solids solution. The epoxy equivalent, on asolids basis, was found to be 137.6 grams per epoxy equivalent,following the procedure outlined by Durbetaki in Analytical Chemistry,volume 28 (1956), page 2000.

Epoxidation may, of course, be carried out in a variety of other ways.For example, the ion exchange resin catalyst and the acetic acid mayboth be replaced with formic acid, the time required for reaction beingreduced to approximately minutes, and the reaction temperature requiredbeing 2l24 C. Similarly, the polybutadiene may be dissolved in1,4-dioxane and the hydrogen peroxide replaced with peracetic acid,employing a somewhat longer reaction time. More complete epoxidation maybe obtained by using perphthalic acid, but this oxidizing agent is quiteexpensive, and hence less attractive commercially.

Conversion of epoxidized rubbery polymer to Water-soluble polymer In a500 ml., three-neck, round-bottomed flask equipped with stirrer, refluxcondenser and nitrogen inlet was placed 248.5 grams of a 7.86% solutionof epoxidized cis-1,4-polybutadiene in 1,4 dioxane, the epoxy equivalentof the rubber being 112.8 grams per epoxy group (i.e., 56.4% of thetheoretical number of double bonds epoxidized). Next was added 15.2grams (0.174 mol) of morpholine and 1.63 grams (0.0174 mol) of phenol.

It is well known that the amination of oxirane rings can be acceleratedby weak hydrogen donors which serve as catalysts. Phenyl and similar lowmolecular weight monohydric alcohols as well as water perform thisfunction. While phenol is generally more active than water, the latteris preferred because it is more easily removed after the reaction iscomplete.

The mixture was stirred and heated on a steam bath for about 18 hours.The reaction mixture was then poured slowly into a large volume ofbenzene in order to precipitate the polymer. The precipitate waspurified by dissolving it in methyl alcohol, re-precipitating inbenzene, and re-dissolving in methyl alcohol. A water solution of thepolymer could be obtained by adding the methyl alcohol solution to waterand boiling the solution to remove the methyl alcohol and trace amountsof benzene present, yielding a clear water solution. Analysis of thepolymer for percent nitrogen gave a value of 2.63 based on solidpolymer, representing the reaction of 25.4% of the available epoxygroups with morpholine, or conversion of 14.1% of the original linkagesto Use of water-soluble rubbery polymer as primer A conventionalnormally tacky and pressure-sensitive adhesive tape, in which theadhesive was coated over the aluminum vapor-deposited surface of a l-milpolyester film and protected with a removable liner, was backsized with6 grains (solids basis) per 24 square inches of a 12% methyl alcoholsolution of the water-soluble polymer in the preceding section of thisexample. (Although the polymer is miscible with water in allproportions, aqueous solutions tend to be more viscous. Additionally,more volatile solvents permit faster drying.) After evaporation of thesolvent, the resulting thin coating displayed excellent adhesion to thepolyester film surface, in marked contrast to most watersolublematerials. This product was used as a splicing tape in the manufactureof photographic film, the aqueous photographic emulsion displayingexcellent adhesion to the thus-primed surface. In the absence of such acoating, it is found that the photographic emulsion tends to flake offduring drying and contaminate the film in surrounding areas. Thebacksize was essentially tack-free, although it displayed some adhesionfor a slightly moist finger.

Preparation of water-soluble normally tacky and pressure-sensitiveadhesive A 26.9% methyl alcohol solution of the epoxidized cis-1,4-polybutadiene:morphoiine reaction product described in a precedingsection of this example, was blended with an equal weight (solids basis)of N,N,N,N'-tetrakis (2- hydroxy propyl) ethylene diamine availablecommercially as Quadrol from the Wyandotte Chemical Company. When knifecoated on a 0.003 inch film of biaxially oriented polyethyleneterephthalate, using an aperture of 0.011 inch above the film, and thesolvent then evaporated, the dried adhesive displayed very high webgrab, or initial adhesiveness. The room temperature adhesiveness wasalso measured on a Polyken Probe'lack Tester by forcing the end of astainless steel rod, having a diameter of 5 mm. with an 0.002-inch crownand a surface finish of 5 microinches, against the surface of theadhesive at a rate of 1 cm./sec. and a pressure of 100 gms./cm. After adwell time of /2 second, the force required to remove the rod at a rateof 1 cm./sec. was measured and found to be 533 grams, which is roughlytwice as great as that for conventional transparent pressure-sensitiveadhesive tape, and about five times as high EPOXIDIZED RUBBER:

stresses, as in packaging operations, it is more important to have highinternal strength, and times of 30 minutes or higher before failure areconsidered desirable.

Double-coated tape made by coating both surfaces of 8-lb. Crystex tissuewith a solution of this adhesive displayed excellent adhesion to almostall surfaces. Because of the adhesives excellent adhesion and watersolubility, tapes of this type offer excellent potential for use as arepulpable splicing tape in paper mills, perhaps even for making highspeed, or flying, splices. A l A-inch square piece of this tape wasplaced between the overlapped ends of two -lb. kraft paper strips,rolled once in each direction with a 4 /21b. rubber roller, and allowedto stand for 5 to 10 minutes. When the two ends of the paper were thenclamped, respectively, in the upper and lower jaws of a tensile tester,the force required to shear the bond measured at a jaw separation rateof 12 inches per minute was found to be 3.2 lbs. Increasing the nitrogencontent of the rubbery polymer tends to decrease its tackiness butincrease its shear strength.

The Quadrol in the composition just described functions as awater-soluble tackifier and plasticizer for the Water-soluble modifiedrubber. Generally speaking, the tackiness of the adhesive is directlyrelated, and the internal strength inversely related to the amount oftackifier present. Other tackifiers which may be employed includepolyoxyethylene glycol having a molecular weight of 400, polyoxyethyleneglycol monophenyl ether, dodecyl aniline, p-n-butoxy phenol, and dodecylphenol. Other plasticizers and tackifiers such as triethanolamine may beemployed. Similarly, antioxidants such as 2,6-di-tert-amylphenol may beincluded in the adhesive.

Tabulated below are examples showing the effect of varying the epoxyequivalent of the modified rubbery cisl,4-polybutadiene, the secondaryamine employed, and the conditions under which the amine and epoxidizedrubbery polymer are reacted. All polymers are water-soluble. Wherenormally tacky and pressure-sensitive adhesives were made from thepolymers by blending equal weights of water-soluble polymer and Quadrol,tackiness and internal strength of the adhesives tested as described inthe preceding example, are also listed.

AMINE REACTION Finished Epoxy Mol ratio, M01 ratio, Water, perproductTaek- Internal equivepoxy: phenol: cent wt. of Temp., Reaction adhesive,iness, strength, Ex alent Amine amine Solvent amine solution C time,hrs.percent N grams minutes 2 110. 5 Morpholine 0. 1 20 95 16 18 0. 1 10 950. 1 10 95 0. 1 10 95 16 do 1.0 Dioxane 0.1 10 95 46 233 6 114. 7Dimothylamine 1. 0 (lo 0. 1 8. 48 90 24 2. 01 625 5. 5 134.2 o 1.0 do.0.1 0.12 88 24 1. 54 130 3.2 114. 7 Dicthylamine 0. 1 8. 48 90 24 1. 10432 5. 2 117.3 Di-n-propylamine 0- 1 10 88 40 212 2. 3 120D1-n-butylam1ne 0. 1 10 90 90 1. 27 662 1. 5 120 Diethanolamine 0. 1 1O90 {)0 2. 44 208 0. 1 123. 5 N -methyl benzyla ne 0. 1 10 88 70 O 0. 8120 Piperidine 0. 1 10 80 20 3. 3 733 2. 3

0 EXAMPLE 17 as for any previously known water-solublepressure-sensitive adhesive.

The internal strength of the adhesive was measured by placingtwo-one-half inch strips of the tape in face-to-face relationship sothat they overlapped each other by onehalf inch, resulting in a mutualadhesive contact area of one-half inch by one-half inch. The overlappedstrips were then pressed together with a weighted roll and tensioned bythe application of a force of 1000 grams applied between the free endsof the two strips. The time for the face-to-face bond to fail by slidingapart was found to be 7.3 minutes. A shear time of 5 minutes isconsidered adequate for most uses to which transparent tape adhesivesare subjected, and even lower values may be satisfactory where the tapeis not to be subjected to stress in use. Where the tape will besubjected to tensile A rubbery 76.5 223.5 butadienezstyrene copolymer,having a Mooney viscosity (ML-4 at 212 F.) of 50-58, available fromShell Chemical Company, under the trade designation GR-S Type 1011Synthetic Rubber, was epoxidized in the same manner as described inExample 1, the ultimate epoxy equivalent obtained being 186.1,representing a conversion of approximately 41.5% of the double bonds toepoxy groups. The raw rubbery copolymer is somewhat harder to epoxidizeto the same degree as cis-1,4-polybutadiene. The epoxidized rubber,although less elastic than the original polymer, was still tough and,when stretched, slowly returned to its original length. Following thesame general procedure outlined in Example 1 (except for the use of 10%water in the catalyst system and the substitution of dimethylamine forthe morpholine), the epoxidized rubbery copolymer was reacted withdimethylamine to obtain a water-soluble rubbery copolymer. When blendedwith an equal weight of Quadrol, the resultant normally tacky andpressuresensitive adhesive had a tackiness value of 158 and an internalstrength of 69.9, when tested as described in Example 1, making ituseful as an adhesive for packaging tape.

EXAMPLE 18 water-soluble by reaction with dimethylamine. Thewatersoluble polymer may be employed as a primer for hydrophobicsubstrates or compounded into an adhesive, as in preceding examples.

EXAMPLES -25 These examples illustrate the rubbery characteristics ofthe water-soluble polymers of this invention and clearly indicate, bycomparison of these characteristics with the characteristics of therubbers before treatment, the similarity in properties. The procedurefor making products of these examples is generally like those used inthe preceding examples with the conditions indicated in the table below,1,4-dioxane being used as the solvent for epoxidized rubber in allcases. It should be noted that While the polyisoprene derivative issoluble, it required a relatively extended period of agitation todissolve completely and form an aqueous solution.

Moles of epoxidation reactants Reaction conditions epoxidation DoubleTemp., Epoxy, Ex. Rubber Amine Epoxidizing agent bond Time C. Solventequiv. wt.

- Formic acid 0.285 cls-lii-pmybutadlene Dlmethyl plus 1. s3 5 hrs., 8min, plus 65-67 Toluene-. 131

mung Hydrogen peroxide. 2.19 hr., 27 min. 21- .do..- Morphollnen Same asabove-.. 2. 19 1. 8 do 124 -do... Piperidine do 2.19 1. 83 do 131Cis-1,4 polyisoprene Dimethyl Peracetic acid plus 0.936 0. 936 2 hrs.,40 mm. 223

(Ameripol SN 600, amine. 4.85 g. anhydrous plus 3 hrs., 49 Mooneyviscosity 75-90). aAc. mm. 24--.. Butadiene:styrene(GR-S .....doPeracctic acid plus 0.527 0.5 17 hrs. plus 2 5-22 Mcthylene 200 Type1011). i168 Ag. anhydrous hrs., mm. chloride.

a c. 25. .3 Butadiene:acrylonitrile do Peracetic acid plus 0. 5 O. 5 6hrs. plus 30 min- 930 -..--do 183 (Hycar 1014). 2.5 g. anhydrous N aAc.

Finish product Reaction conditions-amination Moles of aminationreactants Percent Moles added conversion Temp, N, equiv.- Percent ofepoxy Example Time 0 H2O Phenol wt. N to amine 19 hrs 59-63 1. 3 0.0 4253. 29 34. 5 0 4 16 hrs., 10 min 84 2. 1 0. 02 522 2.68 28. 6 3 hrs., min68-78 1. 6 0.0 482 2.91 33.0 0. 21 hrs., 40 min. plus 66 hrs 63 O. 0 0.0 2640 0. 53 8. 6 0. 12 0.6- 19 s. 71 2.1 0.0 1006 1. 39 20. 8 0. 2 1.0plus 1.0--.- 16 hrs. plus 6.5 hrs 67-69 3. 4 0.0 922 1. 52 20.9

1 600 m1. of methylene chloride was added to redissolve epoxidizedpolymer which precipitated after addition of all peracetic acid. 2 1.2moles of dimethylamiue was added to the mixture after 21 hours, 40minutes; then heating was continued for 66 hours. 8 172 m1. of methanolwas added to dissolve the polymer after 16 hours, at which time another1.0 mole of amine was added.

less elastic than the unmodified polymer, the epoxidized product wasstill tough and fairly elastic. The epoxidized polymer was then madewater-soluble by reacting it with dimethylamine, as in Example 2. Whenblended with an equal weight of Quadrol, the resultant normally tackyand pressure-sensitive adhesive had a tackiness value of 190 and aninternal strength of 33.2 when tested as in Example 1. The presence ofthe polar O group is believed to enhance aflinity of the adhesive formetal surfaces.

EXAMPLE 19 Cis-1,4-polyisoprene (which has basically the same molecularstructure as natural rubber), having a Mooney viscosity (ML-4 at 212 F.)of -95, available commercially from Goodyear Tire & Rubber Company underthe trade designation Natsyn polyisoprene rubber is epoxidized to anepoxy equivalent of 180 and rendered The water-soluble polymers wereprepared for testing polymer, using a nitrogen sweep to speed drying andminimize oxidative attack. Since these polymers are aifected byhumidity, the tests were performed in controlled humidity chambers. (Thestarting rubbers are not so aifected and hence were tested in ambienthumidity conditions.) The testing procedure followed that given in ASTMTest Procedure D4l2-64T using an Instron tester except that thicknessmeasurements used to determine tensile strength were taken at 5 pointsrather than 3 of the bar portions of the dumbbell-shaped samples. Thethickness measurement closest to the break point was used rather than anaverage thickness as indicated in the ASTM procedure. The tables belowprovide a comparison 5 between the base rubbers and their water-solublecounter parts.

PHYSICAL PROPERTIES OF BASE RUBBERS Tensile strength in p.s.i. atvarious elongations Percent Percent elongation set at Rubber 300% Breakat break break Remarks Amcripol CB 220 (compare with Ex. 20-22) 15. 612.4 5. 86 1,406 Break occuired. Ameripol SN 600 (compare with Ex. 23)44.8 37. 7 33. 7 1, 346 312 Do. GR-S Type 1011 (compare with Ex. 24) 31.1 28.9 30. 9 1, 833 258 No break occurred at maximum Instron setting.Hycar 1014 (compare with Ex. 25).-- 51.4 44. 7 41. 7 1, 738 168 Do.

PHYSICAL PROPERTIES OF WATER-SOLUBLE RUBBERS Tensile strength in p.s.i.

at various elongations Percent Percent Relative elongation set at Exhumidity 150% 300% Break at break break Remarks 20.... 35 137 171 366692 5. 4 Break.

60 82 89. 7 167 1, 042 20. 5 Do. 21--- 38 57. 6 65.8 101 1, 366 43. 7Do.

55 44. 3 45. 3 61. 1 942 35. 4 Do. 22.. 35 94. 6 102 137 1, 308 53. 6Do.

50 63. 7 60. 9 1, 800 No break at maximum Instron" setting. 23.-. 35 127189 867 687 3. 1 Break.

50 107 147 622 666 4. 6 D0. 24. 35 1, 270 1, 710 1, 745 325 22. 6 Do.

50 135 189 290 567 9 D0. 25 33 36. 4 40. 5 114. 2 1, 450 181 N 0 breakvalues given at maximum "Instron extension.

25. 8 25. 8 27. 9 60. 2 1, 617 204 Break.

The man skilled in the art will recognize that it is not feasible to setforth all the variations to which this invention is susceptible, andmany modifications will readily suggest themselves. For example, thehigher the molecular weight of the rubbery polymer, the greater thenumber of tertiary amino groups required to induce an equivalent degreeof water-solubility. Likewise, the watersolubilizing ability of a givensecondary amine is enhanced if the amine compound also contains OH orother polar groups. Where it is desired to have a polymer which iswater-soluble but which can be cross-linked to an insoluble state, it ispossible to introduce compounds which react with either two or moreepoxy rings or two or more hydroxyl groups under the stimulus of, e.g.,heat. For example, dihalogen compounds such as ethylene dichloride,dichloromethyl ether, and a,w-dichloropolyoxyethylene may react with thetertiary amino groups, thereby forming water-soluble crosslinking saltbonds. The rate of crosslinking may be suitably controlled by selecteddihalogen compounds having the desired degree of reactivity. Wheredesired, these compounds may be enclosed in capsules which rupture undera predetermined threshold stimulus of heat or pressure. Crosslinking maybe similarly eifected through the OH groups, using glyoxal or aformaldehyde donor such as hexamethylene tetramine. Such adhesivecompositions lend themselves to the preparation of self-sustainingthermosetting pressuresensitive adhesive transfer tapes (i.e., tacky butcurable adhesive films provided with a removable liner), as well asstrong but water-soluble crosslinked adhesives, such as for a repulpablesplicing tape useful in paper mills.

Normally tacky and pressure-sensitive adhesives made with thewater-soluble rubber polymers of the present invention display excellentadhesion to a wide variety of materials, and because such adhesives arealso watersoluble, they stick tenaciously when applied but can beremoved by soaking in water. Adhesives of this type may be employed inthe preparation of Water-activatable labels, thereby making theirapplication simultaneously simple and effective. Because the modifiedrubbery polymers are essentially inert to most organic solvents,adhesives made with the polymers may be useful for attaching labels tofuel lines, hydraulic fluid lines, cooking oil containers, and the like.The hydrophilic nature of pressure-sensitive adhesives of the typedescribed herein also reduces static electricity problems which plaguethe users of many conventional tape products and may eliminate the needfor antistatic backsizes in most situations. The electrical conductivityof these adhesives also suggests their use for holding electrodes inplace in electrocardiographic wor-k. Both the conductivity and thebacteriostatic properties of the adhesive may be enhanced by reacting itwith methyl bromide to form quaternary salts.

1 claim:

1. A water-soluble normally tacky and pressure-sensitive adhesivecomprising a homogeneous blend of (a) a water-soluble rubbery polymer,alkaline in aqueous solution, consisting essentially of the reactionproduct of an epoxidized water-insoluble neutral rubbery polymerselected from the class consisting of cis-1,4-polybutadiene,butadienezstyrene copolymer, butadiene:acrylonitrile copolymer andcis-1,4 polyisoprene and a water-soluble secondary mono amine, with saidepoxidized rubbery polymer having an epoxy equivalent of not greaterthan about 225, and (b) an effective amount of organic tackifying agent.

2. The adhesive of claim 1 wherein the neutral rubbery polymer iscis-l,4-polybutadiene.

3. The adhesive of claim 1 wherein the neutral rubbery polymer is abutadienerstyrene copolymer.

4. The adhesive of claim 1 wherein the neutral rubbery polymer is abutadiene:acrylonitrile copolymer.

5. The adhesive of claim 1 wherein the neutral rubbery polymer iscis-l,4-polyisoprene.

6. The adhesive of claim 1 wherein the secondary mono amine ismorpholine.

7. The adhesive of claim 1 wherein the secondary monoamine is dimethylamine.

8. The pressure-sensitive adhesive of claim 1 wherein the organictackifying agent is N,N,N,N-tetrakis '(2-hydroxypropyl) ethylenediamine.

9. .Normally tacky and pressure-sensitive adhesive tape comprising aflexible sheet backing having firmly bonded to at least one face thereofa layer of the normally tacky and pressure-sensitive adhesive of claim1.

10. Normally tacky and pressure-sensitive adhesive tape comprising aflexible sheet backing having firmly bonded to at least one face thereofa layer of the normally tacky and pressure-sensitive adhesive of claim2..

11. Normally tacky and pressure-sensitive adhesive tape comprising aflexible sheet backing having firmly bonded to at least one face thereofa layer of the normally tacky and pressure-sensitive adhesive of claim3.

12. Normally tacky and pressure-sensitive adhesive tape comprising aflexible sheet backing having firmly bonded to at least one face thereofa layer of the normally tacky and pressure-sensitive adhesive of claim4.

13. Normally tacky and pressure-sensitive adhesive tape comprising aflexible sheet backing having firmly bonded to at least one face thereofa layer of the normally tacky and pressure-sensitive adhesive of claim5.

14. Normally tacky and pressure-sensitive adhesive tape comprising aflexible sheet backing, having firmly bonded to at least one facethereof a layer of the normally tacky and pressure-sensitive adhesive ofclaim 6.

15. Normally tacky and pressure-sensitive adhesive tape comprising aflexible sheet backing having firmly bonded to at least one face thereofa layer of the normally tacky and pressure-sensitive adhesive of claim7.

16. Normally tacky and pressure-sensitive adhesive tape comprising aflexible sheet backing having firmly 1 1 1 2 bonded to at least one facet hereof a layer of the normal- OTHER REFERENCES 1y tacky andpressure-sensltwe adheslve of clalm 8. Technical Data Sheet on Quadrol,Wyandotte Chem References Cited 1959 UNITED STATES PATENTS 5 JOSEPH L.SCHOFER, Primary Examiner 2,952,654 9/1960 Adams et 211. W. F. HAMROCK,Assistant Examiner 3,661,874 5/ 1972 Olson 26094.7 N X US. Cl. X.R.

FOREIGN PATENTS 646,607 8/1962 Canada. 10 26083.3, 85.1, 94.7 N, 122 PA;117122'P; 161-88

